Dialkyl perfluoro-ω-fluoroformyl diesters and monomers and polymers therefrom

ABSTRACT

Diesters of the formula: ##STR1## wherein R is CH 3  or C 2  H 5  and n is 0 to 10; vinyl ether monomers derived therefrom; copolymers of the vinyl ether monomers with one or more selected perfluorinated monoolefins; articles of manufacture made from the copolymers; process for making the diesters; process for using copolymer membranes in a chlor-alkali cell.

BACKGROUND OF THE INVENTION

This invention relates to dialkyl perfluoro-ω-fluoroformyl esters and tomonomers and copolymers made therefrom. Following are descriptions ofseveral background developments which provide a context in which toappreciate the present invention.

Krespan, in South African Pat. No. 77/7158, disclosed O═C(CF₂ CO₂ CH₃)₂,perfluoroalkyl ether dicarboxylates prepared therefrom andperfluorinated copolymers from said dicarboxylates. The perfluoroallylether dicarboxylates are neither homologs nor analogs of theperfluorovinyl ether dicarboxylates described herein.

Selman, in U.S. Pat. No. 3,274,239, disclosed fluoroketones of theformula, XR_(F) C(O)R'_(F) X', where X and X' are H or halogen and R_(F)and R'_(F) are perfluoroalkylene of 1 to 8 carbon atoms;hexafluoropropene oxide (HFPO) adducts thereof,(XR_(F))(X'R'_(F))CFO(CF(CF₃)CF₂ O)_(n) CF(CF₃)COF, where n is 0 to 20;and vinyl ethers formed from said adducts.

England, in U.S. Pat. No. 4,131,740, disclosed the reaction of HFPO witha compound of the formula FOC--CF₂ --CO₂ R in the presence of fluorideion as catalyst and an inert liquid diluent (preferably an organicliquid) in which the selected fluoride is at least 0.001% soluble, toform alkyl perfluoro-ω-fluoroformyl esters, RO₂ CCF₂ (CF₂ O(CF₃)CF)_(n)COF, where n is 0 to 6. Also disclosed are vinyl ethers formed from theesters, and perfluorinated copolymers of the vinyl ethers.

England, in U.S. Pat. No. 4,138,426, disclosed perfluorovinyl ethers,YCF₂ (CF₂ O(CF₃)CF)_(p) CF₂ OCF═CF₂, wherein Y is --CO₂ R, --CO₂ H,--CO₂ M, or --CN; R is 1 to 6 carbons; M is alkali metal, ammonium orquaternary ammonium; and p is 1 to 5.

Breazeale, in U.S. Application Ser. No. 083,751, filed Oct. 22, 1979,disclosed vulcanizable copolymers of tetrafluoroethylene,perfluoromethyl perfluorovinyl ether and a cure site monomer consistingof a cyano-substituted perfluorovinyl ether of the formula, CF₂ ═CF[OCF₂CF(CF₃ ----_(x) O(CF₂)_(n) CN, where n is 1 to 4 and x is 1 or 2.

SUMMARY OF THE INVENTION

This invention concerns dialkyl perfluor-ω-fluoroformyl diesters of theformula: ##STR2## wherein R is CH₃ or C₂ H₅ and n is an integer from 0to 10.

This invention also concerns vinyl ethers derived from 1, said ethershaving the formula: ##STR3## wherein Y is selected from the group CF₂CN, CF₂ CO₂ R, CF₂ CO₂ H, CF₂ CO₂ M, CF₂ CONH₂ and CF₂ CONR₂ ; R and nare as defined above; M is an alkali metal, ammonium or quaternaryammonium.

This invention also concerns copolymers of the vinyl ethers, 2, with oneor more perfluorinated monoolefins selected from the group consisting oftetrafluoroethylene, hexafluoropropylene, perfluoroalkylvinyl etherswherein the alkyl group contains 1 to 4 carbon atoms,chlorotrifluoroethylene, the vinyl ether, CF₂ ═CF[OCF₂ CF(CF₃)]_(m) OCF₂CF₂ SO₂ F, where m is 1 or 2, and mixtures thereof, said copolymerscontaining from about 0.1 to 80 mole percent of vinyl ether, 2. Thisinvention also concerns articles of manufacture made from saidcopolymers, including molded objects and ion-exchange membranes. Thisinvention also concerns a process for producing an alkali metalhydroxide in a chlor-alkali electrolysis cell using an ion-exchangemembrane prepared from said copolymers.

This invention also concerns a process for preparing the diesters, 1, bycontacting dialkyltetrafluoro-3-oxoglutarate, O═C(CF₂ CO₂ R)₂, 3,wherein R is CH₃ or C₂ H₅, with hexafluoropropene oxide (HFPO), ##STR4##in the presence of fluoride ion as catalyst and a solvent for reactantsand catalyst.

DETAILS OF THE INVENTION The Diester Adducts

The dialkyl-tetrafluoro-3-oxoglutarate, 3, is reacted with HFPO in thepresence of fluoride ion as catalyst and a solvent. The fluoride ionsare typically provided by one or more of the following sources: analkali metal flouride, an ammonium fluoride, a sulfonium fluoride suchas benzene sulfonium fluoride and the like. Potassium fluoride ispreferred since its use results in improved product yields. The fluoridecatalyst can be used in amounts of about 0.01 to 10 equivalents,preferably about 0.05 to 0.5 equivalents, per mole of 3.

Suitable solvents are aprotic liquids or mixtures thereof, including theso-called glymes (mono-, di-, tri- and tetraethyleneglycol dimethylether); mononitriles such as aceto-, propio-, butyro- and benzonitrile;dinitriles such as malono-, succino-, glutaro-, adipo-, methylmalono-,pimelo-, subero-, and phthalonitrile; nitrobenzenes; lactones such asγ-butyrolactone, δ-valerolactone and δ-caprolactone. Preferred solventsare mixtures of dinitriles and glymes; especially preferred are mixturesof adiponitrile and tetraglyme in the proportion of about 80 to 98weight percent of adiponitrile and 2 to 20 weight percent of tetraglyme.

The reaction of ketone, 3, with HFPO is exothermic. Reactiontemperatures can range from about 0° to 100° C., with temperaturesbetween 25° and 70° C. being preferred. Pressure is not critical, andsubatmospheric and superatmospheric pressures are operable; pressuresclose to atmospheric are preferred. As illustrated in the Examples,pressure in the reaction vessel is normally controlled by regulating thesupply of gaseous HFPO.

Ketone, 3, is preferably present in substantial excess at the beginningof the reaction. The ketone reacts with 1 or more mols of HFPO to formadducts 1 in which n is 0 (1:1 monoadduct), or a integer of 1 to 10.Adducts wherein n=0 or 1 are preferred; adducts wherein n=1 are mostpreferred. Use of excess ketone, 3, in the reaction improves yields ofthe desired lower adducts (n=0, 1) as well as overall yields of adductsby suppressing formation of HFPO oligomers which are undesiredby-products formed by fluoride ion-catalyzed polymerization of HFPO.

There are several reaction parameters which affect the identity of theparticular adduct that is made. Because adduct solubility tends todecrease in a given solvent as the value of n increases, correspondinglybetter solvents are required to dissolve adducts having high proportionsof HFPO. Also, relatively high temperatures and low HFPO pressures(within the parameters described herein) tend to favor production ofadducts where n is at the lower end of the range, 0 to 10. On the otherhand, to obtain adducts having high n values, it is desirable to employrelatively low temperature and high HFPO pressure.

As explained above, choice of solvent is important relative to the nvalue of the desired adducts. Thus, to produce adducts having high nvalues, solvents of relatively high dissolving power should be employed.In this regard, the glymes are better solvents than the nitriles andsolvent strength can be adjusted by using mixtures of glymes andnitriles in varying proportions.

Choice of solvent also influences the rate at which adducts, 1, areformed by controlling the amount of catalyst in solution; fluoride ionsources such as potassium fluoride are more soluble in the glymes thanin the nitriles. Thus, glyme/nitrile mixed solvents can be tailored forpreferred adducts and for optimum reaction rate. Higher rates of adductformation also improve adduct yields by suppressing the HFPOaligomer-forming side reaction.

To prepare preferred adducts, 1, wherein n=0 or 1, it has been foundthat the reaction proceeds best when a substantial excess of ketone, 3,over HFPO is used and when a solvent mixture is selected in which thesolubility of the desired adduct, and all higher adducts, is relativelylow. Under such conditions, the desired adduct product is removed fromsolution and hence cannot react further with HFPO. In the reaction ofketone, 3, with two moles of HFPO to form the adduct wherein n=1,inevitably the monoadduct (n=0) is also formed as an intermediate andmust be at least partly soluble in the reaction mixture so as to reactwith a further mole of HFPO. The monoadduct so formed may be recycledinto the claimed process, either alone or, preferably, in admixture withketone, 3, as shown in Example 4. Such a mixture may be prepared byadding fresh ketone to the reaction vessel or by recovering themonoadduct and mixing it with a fresh charge of excess ketone and HFPOin a subsequent reaction. Other methods of assuring product optimizationwill be obvious to one skilled in the art from the description providedherein.

THE VINYL ETHERS

The compounds for formula 1 can be pyrolyzed over a solid basic saltsuch as trisodium phosphate, potassium carbonate, or, preferably, sodiumcarbonate, to obtain the corresponding polymerizable vinyl ethermonomers of formula 2': ##STR5## The pyrolysis reaction takes place attemperatures of about 120° to 300° C., preferably 150° to 250° C. in aninert atmosphere, e.g., nitrogen, in the presence of the basic saltswhich have been previously dried by heating to at least 300° C. Themonomeric diesters of formula 2' are converted by known methods intovinyl ether monomers having the following Y₂ values: ##STR6## wherein Rand M are as previously defined.

Monomers of formula 2 can be copolymerized with one or more of thefluorinated vinyl monomers listed above (tetrafluoroethylene, etc.) toyield solid, tough thermoplastic copolymers which can be molded intoshaped articles, including films, and ion exchange membranes forchloralkali electrolysis cells. Alternatively, for polymer usesrequiring ion-exchange capability, the monomer, 2', can be copolymerizedwith said fluorinated vinyl monomers and the copolymer subsequentlyconverted by hydrolysis to the corresponding copolymer containing --CF₂CO₂ H or --CF₂ CO₂ M groups. Formula 2 monomers wherein Y is --CF₂ CNare especially useful for incorporating cure sites into fluoroelastomercompositions.

It will be understood that the vinyl monomers of this invention containtwo especially useful terminal functional groups in addition to thepolymerizable vinyl site. Thus, the present monomers make it possible todouble the functionality of copolymers derived therefrom withoutincreasing the molar percentage of functional monomers in saidcopolymers. Alternatively, copolymer functionality can be maintainedwhile only employing half the molar percentage of functional monomerpreviously necessary.

COPOLYMERS

Copolymers prepared from Formula 2 vinyl monomers contain repeatingunits having the formula ##STR7## where Y and n are as defined above, mis 1 or 2, q is about 1 to 500, r is 0 or about 1 to 5, Z is --F,--R_(F) or --OR_(F) where R_(F) is perfluoroalkyl of 1 to 4 carbonatoms, preferably 1 or 2 carbon atoms, and the X's can all be fluorineor two can be fluorine and one chlorine. Preferred copolymers are thosewherein X and Z are --F, Y is --CF₂ CO₂ R or --CF₂ CN, n is 1 or 2, q is3 to 500, r is 0 or 1 and m is 1. Values of q from 3 to 20 are preferredfor carboxylated copolymers used as electrolysis cell membranes; q of 40to 400 and r=0 are preferred in nitrile-functional fluoroelastomers.Preferred monoolefins for copolymerization with formula 2 vinyl ethersinclude tetrafluoroethylene, hexafluoropropylene, perfluoroalkylvinylethers wherein the alkyl group contains 1 to 4 carbon atoms,chlorotrifluoroethylene, the vinyl ether, CF₂ ═CF[OCF₂ CF(CF₃)]_(m) OCF₂CF₂ SO₂ F, where m is 1 or 2, and mixtures thereof.

In the following Examples parts are by weight unless otherwisespecified. Temperatures are in degrees Centrigrade.

EXAMPLE 1 Reaction of Dimethyl Tetrafluoro-3-Oxyglutarate WithHexafluoropropene Oxide

Cesium fluoride (10 g, 0.18 mol) in a 2 liter 3-neck flask was heated bya Meker burner under vacuum with swirling to dryness. After cooling, theflask was filled with nitrogen and fitted with a thermometer and largemagnetic stirrer. Then, 15 ml of tetraglyme and 19.5 g (0.08 mol) of theabove titled ketoester were added. The flask was evacuated and thenautomatically maintained at about 700 mm (91 kPa) pressure of HFPO.Vigorous stirring resulted in exothermic (54°) absorption of HFPO whichwas arbitrarily stopped after 19 g (0.11 mol) had been absorbed. Twoliquid layers were present in the reaction mixture after HFPOabsorption, indicating reaction products which were insoluble intetraglyme.

Vacuum (ca. 1.0 mm, 130 Pa) was applied to the flask through a liquidnitrogen-cooled trap while heating the flask with steam. The contents ofthe trap were distilled and fractions collected boiling from 30°/15 mm(2 kPa) to 82°/0.2 mm (26 Pa). The higher boiling fractions containedtwo layers due to codistillation of tetraglyme. The fractions arebelieved to have contained adducts, 1, wherein n=0 to 10. By-productHFPO oligomers formed, if any, were present in lower boiling fractionsnot collected.

EXAMPLE 2 ##STR8##

Potassium fluoride (5 g, 0.09 mol) in a 2 liter 3-neck flask was heatedby a Meker burner under vacuum with swirling to dryness. After cooling,the flask was filled with nitrogen and fitted with a thermometer andlarge magnetic stirrer. Then, 2.54 g of tetraglyme(bis[2-(2-methoxyethoxy)ethyl]ether) and 40 ml (48.5 g) of adiponitrilewere added, the flask evacuated and flushed again with nitrogen.Dimethyl tetrafluoro 3-oxoglutarate (MKG) (321 g, 1.3 mol) was added andthe flask evacuated, filled with HFPO and weighed. Stirring was startedand after an induction period of about one hour absorption of HFPObegan, reaching a maximum of about 0.6 g/min and a temperature of 37°.HFPO pressure was automatically maintained at about 700 mm (91 kPa). Theflask was weighed periodically and addition of HFPO was stoppedarbitrarily after 267 g (1.6 mol) had been absorbed.

The contents of the flask were filtered through a sintered glass funnelto remove KF and the filtrate was distilled under vacuum (0.5-1.0 mm; 65to 130 Pa). There was recovered 79.5 g of HFPO oligomers (mostly dimerand trimer) from the Dry Ice-cooled trap on the still and as bottomlayer in the first cuts of recovered MKG. The first cuts boiling up to78°/0.8 mm (104 Pa) after removing bottom layer amounted to 378 g andwere about 50 mol percent of MKG and 50 mol percent (237 g) ofmonoadduct (n=0), dimethyl2,2,3,4,4-pentafluoro-3-(1-fluorocarbonyl-1,2,2,2-tetrafluoroethoxy)pentanedioate,as analyzed by gas chromatography.

There was then obtained 8.6 g of diadduct (n=1), dimethyl2,2,3,4,4-pentafluoro-3-[2-(1-fluorocarbonyl-1,2,2,2-tetrafluoroethoxy)-1,2,2-trifluoro-1-(trifluoromethyl)ethoxy]-pentanediolate,b.p. 86°/1 mm (130 Pa); 12.7 g of triadduct (n=2) dimethyl2,2,3,4,4-pentafluoro-3-[2,3,3,5,6,6,8,9,9,9,-decafluoro-8-fluorocarbonyl-2,5-bis(trifluoromethyl)-1,4,7-trioxanon-1-yl]pentanedioate,b.p. 93°/0.4 mm (52 Pa); 9.0 g of tetraadduct (n=3), dimethyl2,2,3,4,4-pentafluoro-3-[2,3,3,5,6,6,8,9,9,11,12,12,12-tridecafluoro-11-fluorocarbonyl-2,5,8-tris(trifluoromethyl)-1,4,7,10-tetraoxanon-1-yl]pentanedioate,b.p. 103°/0.4 mm (52 Pa) and 150 g of higher boiling material includingadiponitrile. The adiponitrile began to codistill with the adduct andseparated from these fractions as a top layer which was removed beforethe next step. Analytical data and physical properties of the HFPOadducts (n=1,2,3,4) are given in Tables 1 and 2.

EXAMPLE 3

Dimethyl tetrafluoro-3-oxoglutarate (MKG) (124 g, 0.5 mol) was reactedwith HFPO as described in Example 2 using 60 ml of diglyme as solventand 10 g of cesium fluoride plus 3.5 g of potassium fluoride ascatalyst. Reaction was exothermic (53°) after an induction period of 2.5hrs. However, the HFPO absorbed (1099 g, 6.62 mol) was largely convertedto HFPO oligomers. There was isolated 45 g of the monoadduct (n=0), b.p.73°/1.4 mm (182 Pa). Physical and analytical data for the monoadduct aregiven in Tables 1 and 2.

EXAMPLE 4

A mixture of dimethyl tetrafluoro-3-oxoglutarate (MKG) (50 g, 0.2 mol)and its mono-HFPO adduct (50 g, 0.12 mol) were reacted with excess HFPOusing 5 g of HF as catalyst and a mixture of 50 g of adiponitrile and2.6 g of tetraglyme as solvent. After 55 g (0.33 mol) of HFPO had beenabsorbed the mixture consisted of two layers. The bottom layer wasremoved and distilled to give about 52 g of a mixture of 8 mol percentof MKG and 92 mol percent (49 g) of monoadduct (n=0); 11 g of diadduct(n=1); and 14 g of triadduct (n=2).

The reaction was restarted after adding 102 g (0.41 mol) of MKG to thetop layer and was stopped after absorbing 203 g (1.22 mol) of HFPO. Twolayers were again formed. Distillation of the lower layer gave 83 g of amixture of 2 mol percent of MKG and 98 mol percent (81 g) of monoadduct;27 g of diadduct; and 45 g of triadduct.

EXAMPLE 5 ##STR9##

An acid fluoride of the above formula (n=1, 33 ml, 49 g, 0.085 mol)prepared as in Example 2, was added through a syringe driven by a Sagepump at the rate of 0.6 ml/min to a stirred bed of 90 ml of sodiumcarbonate at 190° (previously dried at 400°) under a slow current ofnitrogen. The sodium carbonate was contained in a quartz tube, 2.54 cmdiameter×45.7 cm long, fitted at the top with openings for nitrogen,syringe needle and a motor driven screw running through the bed andheated by a split-type furnace. Product was collected at the bottom ofthe tube.

When addition was complete, vacuum was applied and there was collectedin Dry-Ice--and liquid nitrogen--cooled traps (in series) 38.5 g ofmaterial. Distillation gave 23 g of the above vinyl ether (n=1),dimethyl2,2,3,4,4-pentafluoro-3-[2-(1,2,2-trifluoroethenyloxy)-1,2,2-trifluoro-1-(trifluoromethyl)-ethoxy]pentanedioate,b.p. 77°/0.1 mm (13 Pa). Higher boiling cuts showed the presence of somedecarboxylation product [CF(CF₃)H] in place of CF═CF₂ in the aboveformula]. Physical and analytical data for the vinyl ether are given inTables 1 and 2.

EXAMPLE 6 ##STR10##

An acid fluoride of the above formula (n=2, 20 ml, 34.5 g, 0.046 mol),prepared as in Example 2, was passed through a stirred bed of 90 ml ofsodium carbonate at 202° as described in Example 4. In the same way,22.5 g was recovered giving on distillation 12 g of the vinyl ether(n=2), dimethyl2,2,3,4,4-pentafluoro3[2,3,3,5,6,6,8,9,9-nonafluoro-2,5-bis(trifluoromethyl)-1,4,7-trioxa-8-nonen-1-yl]-pentanedioate,b.p. 87°/0.1 mm (13 Pa). Physical and analytical data for the vinylether are given in Tables 1 and 2.

A higher-boiling impurity was largely the decarboxylation product(CF(CF₃)H in place of CF═CF₂).

EXAMPLE 7 Preparation and Hydrolysis of Copolymer ##STR11##

The vinyl ether monomer prepared in Example 5 (n=1, 10.2 g, 0.02 mol),17.3 g of 1,1,2-trichloro-1,2,2-trifluoroethane (F-113) (distilled undernitrogen), 2.8 g of (0.028 mol) tetrafluoroethylene and 40 μl ofperfluoropropionyl peroxide solution (6% in F-113) were sealed in a 20ml Carius tube (nearly full). After rotating the tube at roomtemperature overnight the polymer was rinsed out and washed on asintered glass funnel with F-113, pressure filtered with nitrogen andvacuum dried in a steam bath to give 1.7 g of white solid. A 7 mil filmwas pressed at 180° and 5 to 6 mil (0.13-0.15 mm) film at 200°/500 psi(3435 kPa). Infrared spectroscopy of the film showed strong estercarbonyl absorption at 5.6 microns. Infrared spectroscopy of a filmremoved from aluminum foil by boiling in 10% sodium hydroxide showedbroad and strong absorption at 2.9 microns and 5.9 microns for COONa.

Vinyl ether monomer was recovered from the above F-113 solution andredistilled. A Carius tube charge of 8.9 g of vinyl ether, 19.7 g of F113, 3.4 g of tetrafluoroethylene and 40 μl of perfluoropropionylperoxide solution treated as above gave 3.2 g of copolymer from which a7 mil (0.18 mm) film was pressed at 220°/500 psi (3435 kPa).

EXAMPLE 8

In a run similar to that of Example 2, starting with 447 g of a mixtureof MKG (35 mol percent) and monoadduct (65 mol percent) recovered fromExample 2, in which 90 g of HFPO was absorbed, there was obtained 35 gof HFPO oligomers, 401 g of starting mixture of MKG and monoadduct (35mol percent of MKG, 65 mol percent of monoadduct (303 g)), 18.1 g ofdiadduct, 11.4 g of triadduct (n=2), 10.3 g of tetraaduct (n=3) and 92.5g of higher-boiling material including adiponitrile.

EXAMPLE 9

Potassium fluoride (1.4 g, 0.024 mol) was placed in a 125 mlround-bottom flask fitted with a magnetic stirrer, dropping funnel, Dryice-cooled condenser and nitrogen inlet, and "flamed out" under nitrogenwith a heat gun. After cooling to 28°, 28.4 g of anhydrous diglyme wasadded to the flask, followed by slow addition, with stirring, ofdimethyl tetrafluoro-3-oxoglutarate (MKG) (29.5 g, 0.12 mol) duringwhich the temperature rose to 33°. Stirring was continued for 1 h afterMKG addition was completed. Almost all the KF dissolved. The flask wasevacuated, then filled with 37 g (0.223 mol) of hexafluoropropene oxide(HFPO). Reaction proceeded at or below 35° for 1.5 h. The reactionmixture, which consisted of two liquid layers, was stirred overnight atroom temperature.

The two layers were separated and weighed: total weight, 89.9 g; lowerlayer, 26.5 g, upper layer, 63.4 g. Vacuum distillation of the upperlayer gave two fractions boiling at (1) 84° to 85°/50 mm (29.9 g) and(2) 85° to 90°/10 mm (23.8 g). Gas chromatography, infrared and nuclearmagnetic resonance analysis showed fraction (1) to be largely diglyme,and fraction (2) to contain the monoadduct ##STR12##

EXAMPLE 10

Potassium fluoride, (5.0 g, 0.09 mol) was added to a 125 ml flask fittedas described in Example 9 and heated under nitrogen. Butyrolactone (45.0g) and dimethyl tetrafluoro-3-oxoglutarate (MKG) (22.4 g, 0.091 mol)were then added, with stirring, followed by hexafluoropropene oxide(HFPO) (26.0 g, 0.157 mol). Moderately rapid reaction occurred and thetemperature rose to 30° to 40°. The reaction mixture consisted of solidsand two liquid layers. The solids were filtered off and the liquidlayers were separated and weighed: total liquid weight, 89.0 g; lowerlayer, 65.6 g, upper layer, 23.4 g. Gas chromatographic analysis showedthat the lower layer contained unreacted MKG, butyrolactone, HFPOoligomers and compounds of the formula ##STR13## and 3 (mono-, di-, tri-and tetraadducts).

EXAMPLE 11 ##STR14##

The vinyl ether prepared as in Example 5 (n=1; 16.0 g, 0.031 mol),1,1,2-trichloro-1,2,2-trifluoroethane (23.5 g), Percadox 16(bis[4-t-butylcyclohexyl]peroxydicarbonate, Noury Chemical Co.; 0.05 g)and tetrafluoroethylene (about 20 g, 0.20 mol) were heated in astainless steel tube at 45° (4 h), 50° (30 min) and 55° (30 min). Thecolorless/milky polymeric gel product was washed three times withacetone, filtered and dried in a vacuum oven. The white product weighed110.1 g. A 2.4 mil film was pressed at 225° from which an infraredspectrum was obtained consistent with that of a copolymer of the abovestructure.

The copolymer had an equivalent weight of 746 as determined by nuclearmagnetic resonance in the following manner at 275°. Signals wereobtained in the -79 ppm region, the -115 to -120 ppm region and the -134ppm region using a CCl₃ F standard corresponding to the CF₂ O/CF₃groups, CF groups and OCF groups, respectively. The integrals were 19.0for the -79 ppm region (CF₂ O/CF₃) and 187.5 for the rest of thespectrum. The equivalent weight of the polymer was calculated asfollows.

Each comonomer unit contains 5 fluorine atoms in CF₂ O or CF₃ groups,(a). Thus, each fluorine is equal to 19.0/5=3.8 integral units. The restof the polymer contains 187.5 integral units arising from othercomonomer fluorine atoms and fluorine atoms originally found intetrafluoroethylene, (TFE). The remaining nine fluorine atoms from thecomonomer, (b), are equal to 9×3.8=34.2 integral units. The fluorineatoms arising from TFE are equal to 187.5-34.2=153.3 integral unitswhile those from the comonomer are equal to 34.2+19=53.2 integral units.Therefore, the molar ratio of TFE to comonomer equals ##EQU1## or 5.04moles of TFE per 0.5 mole of comonomer. Since the molecular weight ofthe comonomer is 484 as the free dicarboxylic acid, the equivalentweight=5.04 (100)+484 (0.5)=746 (or 1.34 meq H⁺ /g). Thus, q in theabove formula is 10 (5.04×2).

EXAMPLE 12

Vinyl ethers, CF₂ ═CFOCF₂ CF(CF₃)OCF₂ CF₂ SO₂ F, (18.9 g, 0.042 mol),CF₂ ═CF[OCF₂ CF(CF₃)]₂ OCF(CF₂ CO₂ CH₃)₂ prepared as in Example 6 (11.2g, 0.028 mol), Percadox 16 (Noury Chemical Co., 0.05 g),1,1,2-trichloro-1,2,2-trifluoroethane (46.9 g) and tetrafluoroethylene(about 24 g, 0.24 mol) were heated in a stainless steel tube asdescribed in Example 11. The white polymer product, after washing inacetone, filtering and drying, weighed 23.4 g. A clear film was pressedbetween Teflon® plates at 250°. Its infrared spectrum was consistentwith that of a terpolymer of the above vinyl ethers andtetrafluoroethylene.

UTILITY

An ion-exchange resin of the copolymer of Example 11 in film form wasprepared as follows: 2.0 g of the copolymer, 50 ml of methanol and 7.5 gof potassium hydroxide were placed in a 100 ml round bottom flask fittedwith a magnetic stirrer and water-cooled condenser and heated to refluxunder nitrogen for 16 h. The flask was then cooled and a gel-likepolymer was collected by filtration, washed thoroughly with anhydrousmethanol and dried in a vacuum oven. Analysis showed that the polymerwas in the form of its potassium (alkali metal) salt. A film of thepolymer, pressed at 250° C., was clear.

The carboxyl-functional perfluorinated copolymers of this invention arecontemplated for use as cation exchange membranes in chlor-alkali cells.For that utility, the carboxyl-containing membranes would be hydrolyzedto convert the carboxyl groups to the sodium (alkali metal) salt form.In their sodium salt form, the membranes would perform their essentialfunction of permitting migration of sodium cations from the anodecompartment to the cathode compartment while preventing the migration ofchloride ions from the anode compartment to the cathode compartment.

Vinyl ether monomers of this invention are useful in the vulcanizationof fluoroelastomers. Copolymerization of vinyl ether monomers of formula2 wherein Y is CF₂ CN with selected perfluorinated monomers such as TFEand perfluoromethylvinyl ether provides curable copolymers which, whenheated in the presence of substances known to promote the formation oftriazine rings by trimerization of nitriles, become cured (vulcanized)fluoroelastomers.

                  TABLE 1                                                         ______________________________________                                        INFRARED, BOILING POINT AND ANALYTICAL DATA                                   ______________________________________                                         ##STR15##                                                                    Infrared                                                                      wave length                                                                   microns                                                                                  F       OCH.sub.3                                                                            Boiling Point                                                                           Refractive Index                          Ex.  n     CO      CO     °C./mm(Pa)                                                                       n.sub.D.sup.25                            ______________________________________                                        3    0     5.30    5.55   73/1.4(182)                                                                             1.3468                                    2    1     5.30    5.55   86/1.0(130)                                                                             1.3370                                    2    2     5.30    5.55   93/0.4(52)                                                                              1.3287                                    2    3     5.30    5.55   103/0.4(52)                                                                             1.3230                                    ______________________________________                                        Analyses                                                                      Calculated     Found                                                          Ex.  C      H      F     C     H     F    Formula                             ______________________________________                                        3    29.14  1.47   46.10 29.25 1.80  46.09                                                                              C.sub.10 H.sub.6 F.sub.10                                                     O.sub.6                             2    27.00  1.05   52.58 27.96 1.47  52.49                                                                              C.sub.13 H.sub.6 F.sub.16                                                     O.sub.7                             2    25.82  0.81   56.17 26.69 0.93  56.27                                                                              C.sub.16 H.sub.6 F.sub.22                                                     O.sub.8                             2    25.07  0.66   58.44 24.99 0.89  59.43                                                                              C.sub.19 H.sub.6 F.sub.28                                                     O.sub. 9                            ______________________________________                                         ##STR16##                                                                    Infrared                                                                      wave length                                                                   microns                                                                                   F        OCH.sub.3                                                                            Boiling Point                                                                           Neut. Equiv.                            Ex.  n      CO       CO     °C./mm(Pa)                                                                       of Acid                                 ______________________________________                                        4    1      5.40     5.55   77/0.1(13)                                                                              242                                     5    2      5.38     5.55   87/0.1(13)                                                                              325                                     ______________________________________                                        Analyses                                                                      Calculated    Found                   Mol                                     Ex.  C      H      F    C    H    F    Formula  Wt                            ______________________________________                                        4    28.14  1.18   51.94                                                                              28.78                                                                              1.43 51.87                                                                              C.sub.12 H.sub.6 F.sub.14 O.sub.6                                                      512                           5    26.56  0.89   56.03                                                                              26.54                                                                              1.02 56.12                                                                              C.sub.15 H.sub.6 F.sub.20 O.sub.7                                                      678                           ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        NUCLEAR MAGNETIC RESONANCE DATA                                               Proton magnetic resonance spectra were                                        obtained with a Varian A-60 spectrometer operating at                         60 MHz; chemical shifts are reported in ppm from tetra-                       methylsilane as external standard with downfield                              direction taken as positive. .sup.19 F magnetic resonance                     spectra were obtained with a Varian A 56/60 spectro-                          meter operating at 56.4 MHz; chemical shifts are                              reported.                                                                     ______________________________________                                         ##STR17##                                                                    Chemical Shifts δ ppm                                                   Ex.  n     CH.sub.3                                                                             COF   CF.sub.3                                                                            CF.sub.2 O                                                                           CF.sub.2 (4F)                                                                        CF                                ______________________________________                                        3    0     3.70   +26.98                                                                              -82.16       -115.80                                                                              -124.86                                                                       -138.85                           2    1     3.70   +26.57                                                                              -79.18                                                                              -79(1F)                                                                              -115.84                                                                              -130.55                                                         broad                                                                   -82.15                                                                              -85(1F)       -135.59                                                         broad         -138.14                           2    2     3.67   + 26.41                                                                             -79.21                                                                              -79(2F)                                                                              -115.83                                                                              -130.59                                                         broad                                                                   -80.09                                                                              -85(2F)       -135.46                                                         broad                                                                   -82.28              -138.01                                                                       -145.04                           2    3     3.65   +26.30                                                                              -79.33                                                                              -79(3F)                                                                              -115.91                                                                              -130.73                                                         broad                                                                   -80.17                                                                              -85(3F)       -135.48                                                   (6F)  broad                                                                   -82.37              -138.73                                                                       -144.91                                                                       (2F)                              ______________________________________                                         ##STR18##                                                                                                Coupling                                                                      constants                                         Chemical Shifts δ ppm for CF                                            Ex.  n     CH.sub.3                                                                             CF.sub.3                                                                            CF.sub.2 O                                                                          CF.sub.2 (4F)                                                                        CF     J.sub.FF in                       ______________________________________                                                                                    Hz                                4    1     3.68   -79.32                                                                              -84.06                                                                              -115.93                                                                              -114.68                                                                              85.6(d),                                                                      65.6(d)                                                                -122.47                                                                              112(d),                                                                       85.6(d),                                                                      6.2(t)                                                                 -136.12                                                                              112(d),                                                                       65.6(d)                                                                       6.2(t)                                                                 -138.35                                                                       -135.30                                  5    2     3.68   -79.20                                                                              -79.48                                                                              -115.81                                                                              -114.55                                                                              86.8(d),                                                                      66.8(d),                                                                      6.2(d)                                              -80.14                                                                              -84.69       -122.41                                                                              111(d),                                                                       86.8(d),                                                                      6.0(t)                                                                 -136.35                                                                              111(d),                                                                       66.8(d),                                                                      4.0(t),                                                                       2.0(d)                                                                 -135.25                                                                       -138.18                                  ______________________________________                                    

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A diester of theformula: ##STR19## wherein R is CH₃ or C₂ H₅ and n is an integer from 0to
 10. 2. A diester according to claim 1 wherein R is CH₃.
 3. A diesteraccording to claim 1 wherein R is C₂ H₅.
 4. A diester according to claim2 or claim 3 wherein n is
 0. 5. A diester according to claim 2 or claim3 wherein n is 1.